Audio Video Transport WG Q. Xie Internet-Draft D. Pearce Expires: August 6, 2004 Motorola February 06, 2004 RTP Payload Formats for European Telecommunications Standards Institute (ETSI) European Standard ES 202 050, ES 202 211, and ES 202 212 Distributed Speech Recognition Encoding draft-ietf-avt-rtp-dsr-codecs-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 6, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document specifies RTP payload formats for encapsulating ETSI Standard ES 202 050 DSR Advanced Front-end (AFE), ES 202 211 DSR Extended Front-end (XFE), and ES 202 212 DSR Extended Advanced Front-end (XAFE) signal processing feature streams for distributed speech recognition (DSR) systems. Xie & Pearce Expires August 6, 2004 [Page 1] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Table of Contents 1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 ETSI ES 202 050 Advanced DSR Front-end Codec . . . . . . . . 4 2.2 ETSI ES 202 211 Extended DSR Front-end Codec . . . . . . . . 4 2.3 ETSI ES 202 212 Extended Advanced DSR Front-end Codec . . . 5 3. DSR RTP Payload Formats . . . . . . . . . . . . . . . . . . 5 3.1 Payload Format for ES 202 050 DSR . . . . . . . . . . . . . 5 3.1.1 Consideration on Number of FPs in Each RTP Packet . . . . . 6 3.1.2 Support for Discontinuous Transmission . . . . . . . . . . . 6 3.1.3 Frame Pair Formats . . . . . . . . . . . . . . . . . . . . . 6 3.1.4 RTP header usage . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Payload Format for ES 202 211 DSR . . . . . . . . . . . . . 8 3.2.1 Consideration on Number of FPs in Each RTP Packet . . . . . 9 3.2.2 Support for Discontinuous Transmission . . . . . . . . . . . 9 3.2.3 Frame Pair Formats . . . . . . . . . . . . . . . . . . . . . 9 3.2.4 RTP header usage . . . . . . . . . . . . . . . . . . . . . . 11 3.3 Payload Format ES 202 212 DSR . . . . . . . . . . . . . . . 12 3.3.1 Consideration on Number of FPs in Each RTP Packet . . . . . 12 3.3.2 Support for Discontinuous Transmission . . . . . . . . . . . 12 3.3.3 Frame Pair Formats . . . . . . . . . . . . . . . . . . . . . 12 3.3.4 RTP header usage . . . . . . . . . . . . . . . . . . . . . . 15 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . 15 4.1 Mapping MIME Parameters into SDP . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . 17 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 17 Normative References . . . . . . . . . . . . . . . . . . . . 17 Informative References . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . 20 Xie & Pearce Expires August 6, 2004 [Page 2] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 1. Conventions The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [5]. The following acronyms are used in this document: DSR - Distributed Speech Recognition ETSI - the European Telecommunications Standards Institute FP - Frame Pair DTX - Discontinuous Transmission VAD - Voice Activity Detection 2. Introduction Distributed speech recognition (DSR) technology is intended for a remote device acting as a thin client, also known as the front-end, to communicate with a speech recognition server, also called a speech engine, over a network connection to obtain speech recognition services. More details on DSR over Internet can be found in [10]. To achieve interoperability with different client devices and speech engines, the first ETSI standard DSR front-end ES 201 108 was published in early 2000 [11], and an RTP packetization for ES 201 108 frames is defined in [10] in IETF. In ES 202 050 [1], ETSI issues another standard for an Advanced DSR front-end that provides substantially improved recognition performance when background noise is present. The codecs in ES 202 050 uses a slightly different frame format from that of ES 201 108 and thus the two do not inter-operate with each other. The RTP packetization for ES 202 050 front-end defined in this document uses the same RTP packet format layout as that defined in [10]. The differences are in the DSR codec frame bit definition and the payload type MIME registration. The two further standards, ES 202 211 and ES 202 212, provided extensions to each of the DSR front-end standards. The extensions allow the speech waveform to be reconstructed for human audition and can also be used to improve recognition performance for tonal languages. This is done by sending additional pitch and voicing information for each frame along with the recognition features. The RTP packet format for these extended standards are also defined Xie & Pearce Expires August 6, 2004 [Page 3] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 in this document. 2.1 ETSI ES 202 050 Advanced DSR Front-end Codec Some relevant characteristics of ES 202 050 Advanced DSR front-end codec are summarized below. The front-end calculation is a frame-based scheme that produces an output vector every 10 ms. In the front-end feature extraction, noise reduction by two stages of Wiener filtering is performed first. Then, waveform processing is applied to the de-noised signal and mel-cepstral features are calculated. At the end, blind equalization is applied to the cepstral features. The front-end algorithm produces at its output a mel-cepstral representation in the same format as ES 210 108, i.e., 12 cepstral coeffients [C1 - C12], C0 and log Energy. Voice activity detection (VAD) for the classification of each frame as speech or non-speech is also implemented in Feature Extraction. The VAD information is included in the payload format for each frame pair to be sent to the remote recognition engine as part of the payload. This information may optionally be used by the receiving recognition engine to drop non-speech frames. The front-end supports three raw sampling rates: 8 kHz, 11 kHz, and 16 kHz (It is worthwhile to note that unlike some other speech codecs, the feature frame size of DSR presented to RTP packetization is not dependent on the number of speech samples used in each 10 ms sample frame. This will become more evident in the following sections). After calculation of the mel-cepstral representation, the representation is first quantized via split-vector quantization to reduce the data rate of the encoded stream. Then, the quantized vectors from two consecutive frames are put into an FP, as described in more detail in Section 4.1 below. 2.2 ETSI ES 202 211 Extended DSR Front-end Codec Some relevant characteristics of ES 202 211 Extended DSR front-end codec are summarized below. ES 202 211 is an extension of the mel-cepstrum DSR Front-end standard ES 201 108 [11]. The mel-cepstrum front-end provides the features for speech recognition but these are not available for human listening. The purpose of the extension is allow the reconstruction of the speech waveform from these features so that they can be replayed. The front-end feature extraction part of the processing is exactly the same as for ES 201 108. To allow speech reconstruction additional fundamental frequency (perceived as pitch) and voicing class (e.g. non-speech, voiced, unvoiced and mixed) information is needed. This is the extra information that is provided by the extended front-end Xie & Pearce Expires August 6, 2004 [Page 4] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 processing algorithms at the device side that is compressed and transmitted along with the front-end features to the server. This extra information may also be useful for improved speech recognition performance with tonal languages such as Mandarin, Cantonese and Thai. Full information about the client side signal processing algorithms used in the standard are described in the specification ES 202 211 [2]. The additional fundamental frequency and voicing class information is compressed for each frame pair. The pitch for the first frame of the FP is quantised to 7 bits and the second frame is differentially quantized with 5 bits. The voicing class is indicated with one bit for each frame. The total for the extension information for a frame pair therefore consists of 14 bits plus and additional 2 bits of CRC error protection computed over these extension bits only. The total information for the frame pair is made up of 92 bits for the two compressed front-end feature frames (including 4 bits for their CRC) plus 16 bits for the extension (including 2 bits for their CRC) and 4 bits of null padding to give a total of 14 octets per frame pair. As for ES 201 208 the extended frame pair also corresponds to 20ms of speech. The extended front-end supports three raw sampling rates: 8 kHz, 11 kHz, and 16 kHz. The quantized vectors from two consecutive frames are put into an FP, as described in more detail in Section 4.1 below. The parameters received at the remote server from the RTP extended DSR payload specified here can be used to synthesize an intelligible speech waveform for replay. The algorithms to do this are described in the specification ES 202 211 [2]. 2.3 ETSI ES 202 212 Extended Advanced DSR Front-end Codec ES 202 212 is the extension for the DSR Advanced Front-end ES 202 050 [1]. It provides the same capabilities as the extended mel-cepstrum front-end described in section 2.2 but for the DSR Advanced Front-end. 3. DSR RTP Payload Formats 3.1 Payload Format for ES 202 050 DSR An ES 202 050 DSR RTP payload datagram uses exactly the same layout as defined in Section 3 of [10], i.e., a standard RTP header followed by a DSR payload containing a series of DSR FPs. Xie & Pearce Expires August 6, 2004 [Page 5] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 The size of each ES 202 050 FP is still 96 bits or 12 octets (see Sections 4 below). This ensures that a DSR RTP payload will always end on an octet boundary. 3.1.1 Consideration on Number of FPs in Each RTP Packet Same considerations described in Section 3.1 of [10] apply to ES 202 050 RTP payload. 3.1.2 Support for Discontinuous Transmission Same considerations described in Section 3.2 of [10] apply to ES 202 050 RTP payload. 3.1.3 Frame Pair Formats 3.1.3.1 Format of Speech and Non-speech FPs The following mel-cepstral frame MUST be used, as defined in [1]: As defined in [1], pairs of the quantized 10ms mel-cepstral frames MUST be grouped together and protected with a 4-bit CRC, forming a 92-bit long FP. At the end, each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in order to make the FP aligned to the 32-bit word boundary. The following diagram shows a complete ES 202 050 FP: Frame #1 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(2,3) | idx(0,1) | Octet 1 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(4,5) | idx(2,3) (cont) : Octet 2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(6,7) |idx(4,5)(cont) Octet 3 +-----+-----+-----+-----+-----+-----+-----+-----+ idx(10,11)| VAD | idx(8,9) | Octet 4 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(12,13) | idx(10,11) (cont) : Octet 5 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) (cont) : Octet 6/1 +-----+-----+-----+-----+ Xie & Pearce Expires August 6, 2004 [Page 6] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Frame #2 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ : idx(0,1) | Octet 6/2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(2,3) |idx(0,1)(cont) Octet 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(6,7) | idx(4,5) | Octet 8 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(8,9) | idx(6,7) (cont) : Octet 9 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(10,11) | VAD |idx(8,9)(cont) Octet 10 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) | Octet 11 +-----+-----+-----+-----+-----+-----+-----+-----+ CRC for Frame #1 and Frame #2 and padding in FP: ================================================ (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ | 0 | 0 | 0 | 0 | CRC | Octet 12 +-----+-----+-----+-----+-----+-----+-----+-----+ The 4-bit CRC in the FP MUST be calculated using the formula (including the bit-order rules) defined in 7.2 in [1]. Therefore, each FP represents 20ms of original speech. Note, as shown above, each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in order to make the FP aligned to the 32-bit word boundary. This makes the total size of an FP 96 bits, or 12 octets. Note, this padding is separate from padding indicated by the P bit in the RTP header. The definition of the indices and 'VAD' flag are described in [1] and their value is only set and examined by the codecs in the front-end client and the recognizer. Any number of FPs MAY be aggregate together in an RTP payload and they MUST be consecutive in time. However, one SHOULD always keep the RTP payload size smaller than the MTU in order to avoid IP fragmentation and SHOULD follow the recommendations given in Section 3.1 in [10] when determining the proper number of FPs in an RTP payload. Xie & Pearce Expires August 6, 2004 [Page 7] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 3.1.3.2 Format of Null FP Null FPs are sent to mark the end of a transmission segment. Details on transmission segment and the use of Null FPs can be found in [10]. A Null FP for the ES 202 050 front-end codec is defined by setting the content of the first and second frame in the FP to null (i.e., filling the first 88 bits of the FP with 0's). The 4-bit CRC MUST be calculated the same way as described in 7.2.4 in [1], and 4 zeros MUST be padded to the end of the Null FP to made it 32-bit word aligned. 3.1.4 RTP header usage The format of the RTP header is specified in [8]. This payload format uses the fields of the header in a manner consistent with that specification. The RTP timestamp corresponds to the sampling instant of the first sample encoded for the first FP in the packet. The timestamp clock frequency is the same as the sampling frequency, so the timestamp unit is in samples. As defined by ES 202 050 front-end codec, the duration of one FP is 20 ms, corresponding to 160, 220, or 320 encoded samples with sampling rate of 8, 11, or 16 kHz being used at the front-end, respectively. Thus, the timestamp is increased by 160, 220, or 320 for each consecutive FP, respectively. The DSR payload for ES 202 050 front-end codes is always an integral number of octets. If additional padding is required for some other purpose, then the P bit in the RTP in the header may be set and padding appended as specified in [8]. The RTP header marker bit (M) should be set following the general rules for audio codecs as defined in Section 4.1 in [9]. The assignment of an RTP payload type for this new packet format is outside the scope of this document, and will not be specified here. It is expected that the RTP profile under which this payload format is being used will assign a payload type for this encoding or specify that the payload type is to be bound dynamically. 3.2 Payload Format for ES 202 211 DSR An ES 202 211 DSR RTP payload datagram is very similar to that defined in Section 3 of [10], i.e., a standard RTP header followed by a DSR payload containing a series of DSR FPs. Xie & Pearce Expires August 6, 2004 [Page 8] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 The size of each ES 202 211 FP is 112 bits or 14 octets (see Sections 4 below). This ensures that a DSR RTP payload will always end on an octet boundary. 3.2.1 Consideration on Number of FPs in Each RTP Packet Same considerations described in Section 3.1 of [10] apply to ES 202 211 RTP payload. 3.2.2 Support for Discontinuous Transmission Same considerations described in Section 3.2 of [10] apply to ES 202 211 RTP payload. 3.2.3 Frame Pair Formats 3.2.3.1 Format of Speech and Non-speech FPs The following mel-cepstral frame MUST be used, as defined in Section 6.2.4 in [2]: As defined in Section 6.2.4 in [2], after two frames (Frame #1 and Frame #2) worth of codebook indices, or 88 bits, a 4-bit CRC calculated on these 88 bits immediately follows it. The pitch indices of the first frame (Pidx1: 7 bits) and the second frame (Pidx2: 5 bits) of the frame pair then follow. The class indices of the two frames in the frame pair worth 1 bit each (Cidx1 and Cidx2) next follow. Finally, a 2-bit CRC calculated on the pitch and class bits (total: 14 bits) of the frame pair using the binary polynomial g(X) = 1 + X + X2 is included (PC-CRC). The total number of bits in frame pair packet is therefore 44 + 44 + 4 + 7 + 5 + 1 + 1 + 2 = 108. At the end, each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in order to make the FP aligned to the 32-bit word boundary. The following diagram shows a complete ES 202 211 FP: Xie & Pearce Expires August 6, 2004 [Page 9] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Frame #1 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(2,3) | idx(0,1) | Octet 1 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(4,5) | idx(2,3) (cont) : Octet 2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(6,7) |idx(4,5)(cont) Octet 3 +-----+-----+-----+-----+-----+-----+-----+-----+ idx(10,11) | idx(8,9) | Octet 4 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(12,13) | idx(10,11) (cont) : Octet 5 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) (cont) : Octet 6/1 +-----+-----+-----+-----+ Frame #2 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ : idx(0,1) | Octet 6/2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(2,3) |idx(0,1)(cont) Octet 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(6,7) | idx(4,5) | Octet 8 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(8,9) | idx(6,7) (cont) : Octet 9 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(10,11) |idx(8,9)(cont) Octet 10 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) | Octet 11 +-----+-----+-----+-----+-----+-----+-----+-----+ CRC for Frame #1 and Frame #2 in FP: ==================================== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ | CRC | Octet 12/1 +-----+-----+-----+-----+ Xie & Pearce Expires August 6, 2004 [Page 10] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Extension information and padding in FP: ======================================== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ : Pidx1 | Octet 12/2 +-----+-----+-----+-----+-----+-----+-----+-----+ | Pidx2 | Pidx1 (cont) : Octet 13 +-----+-----+-----+-----+-----+-----+-----+-----+ | 0 | 0 | 0 | 0 | PC-CRC |Cidx2|Cidx1| Octet 14 +-----+-----+-----+-----+-----+-----+-----+-----+ The 4-bit CRC and the 2-bit PC-CRC in the FP MUST be calculated using the formula (including the bit-order rules) defined in 6.2.4 in [2]. Therefore, each FP represents 20ms of original speech. Note, as shown above, each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in order to make the FP aligned to the 32-bit word boundary. This makes the total size of an FP 112 bits, or 14 octets. Note, this padding is separate from padding indicated by the P bit in the RTP header. Any number of FPs MAY be aggregate together in an RTP payload and they MUST be consecutive in time. However, one SHOULD always keep the RTP payload size smaller than the MTU in order to avoid IP fragmentation and SHOULD follow the recommendations given in Section 3.1 in [10] when determining the proper number of FPs in an RTP payload. 3.2.3.2 Format of Null FP A Null FP for the ES 202 211 front-end codec is defined by setting all the 112 bits of the FP with 0's. Null FPs are sent to mark the end of a transmission segment. Details on transmission segment and the use of Null FPs can be found in [10]. 3.2.4 RTP header usage The format of the RTP header is specified in [8]. This payload format uses the fields of the header in a manner consistent with that specification. The RTP timestamp corresponds to the sampling instant of the first sample encoded for the first FP in the packet. The timestamp clock frequency is the same as the sampling frequency, so the timestamp unit is in samples. As defined by ES 202 211 front-end codec, the duration of one FP is Xie & Pearce Expires August 6, 2004 [Page 11] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 20 ms, corresponding to 160, 220, or 320 encoded samples with sampling rate of 8, 11, or 16 kHz being used at the front-end, respectively. Thus, the timestamp is increased by 160, 220, or 320 for each consecutive FP, respectively. The DSR payload for ES 202 211 front-end codes is always an integral number of octets. If additional padding is required for some other purpose, then the P bit in the RTP in the header may be set and padding appended as specified in [8]. The RTP header marker bit (M) should be set following the general rules for audio codecs as defined in Section 4.1 in [9]. The assignment of an RTP payload type for this new packet format is outside the scope of this document, and will not be specified here. It is expected that the RTP profile under which this payload format is being used will assign a payload type for this encoding or specify that the payload type is to be bound dynamically. 3.3 Payload Format ES 202 212 DSR Similar to other ETSI DSR front-end encoding schemes, the encoded DSR feature stream of ES 202 212 is transmitted in a sequence of frame pairs (FPs), where each FP represents two consecutive original voice frames. An ES 202 212 DSR RTP payload datagram is very similar to that defined in Section 3 of [10], i.e., a standard RTP header followed by a DSR payload containing a series of DSR FPs. The size of each ES 202 212 FP is 112 bits or 14 octets (see Sections 3 below). This ensures that an ES 202 212 DSR RTP payload will always end on an octet boundary. 3.3.1 Consideration on Number of FPs in Each RTP Packet Same considerations described in Section 3.1 of [10] apply to ES 202 212 RTP payload. 3.3.2 Support for Discontinuous Transmission Same considerations described in Section 3.2 of [10] apply to ES 202 212 RTP payload. 3.3.3 Frame Pair Formats Xie & Pearce Expires August 6, 2004 [Page 12] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 3.3.3.1 Format of Speech and Non-speech FPs The following mel-cepstral frame MUST be used, as defined in Section 7.2.4 in [3]: As defined in Section 7.2.4 in [3], after two frames (Frame #1 and Frame #2) worth of codebook indices, or 88 bits, a 4-bit CRC calculated on these 88 bits immediately follows it. The pitch indices of the first frame (Pidx1: 7 bits) and the second frame (Pidx2: 5 bits) of the frame pair then follow. The class indices of the two frames in the frame pair worth 1 bit each next follow (Cidx1 and Cidx2). Finally, a 2-bit CRC (PC-CRC) calculated on the pitch and class bits (total: 14 bits) of the frame pair using the binary polynomial g(X) = 1 + X + X2 is included. The total number of bits in frame pair packet is therefore 44 + 44 + 4 + 7 + 5 + 1 + 1 + 2 = 108. At the end, each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in order to make the FP aligned to the 32-bit word boundary. The padding brings the total size of a FP to 112 bits, or 14 octets. Note, this padding is separate from padding indicated by the P bit in the RTP header. The following diagram shows a complete ES 202 212 FP: Frame #1 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(2,3) | idx(0,1) | Octet 1 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(4,5) | idx(2,3) (cont) : Octet 2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(6,7) |idx(4,5)(cont) Octet 3 +-----+-----+-----+-----+-----+-----+-----+-----+ idx(10,11)| VAD | idx(8,9) | Octet 4 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(12,13) | idx(10,11) (cont) : Octet 5 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) (cont) : Octet 6/1 +-----+-----+-----+-----+ Xie & Pearce Expires August 6, 2004 [Page 13] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Frame #2 in FP: =============== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ : idx(0,1) | Octet 6/2 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(2,3) |idx(0,1)(cont) Octet 7 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(6,7) | idx(4,5) | Octet 8 +-----+-----+-----+-----+-----+-----+-----+-----+ : idx(8,9) | idx(6,7) (cont) : Octet 9 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(10,11) | VAD |idx(8,9)(cont) Octet 10 +-----+-----+-----+-----+-----+-----+-----+-----+ | idx(12,13) | Octet 11 +-----+-----+-----+-----+-----+-----+-----+-----+ CRC for Frame #1 and Frame #2 in FP: ==================================== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ | CRC | Octet 12/1 +-----+-----+-----+-----+ Extension information and padding in FP: ======================================== (MSB) (LSB) 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+ : Pidx1 | Octet 12/2 +-----+-----+-----+-----+-----+-----+-----+-----+ | Pidx2 | Pidx1 (cont) : Octet 13 +-----+-----+-----+-----+-----+-----+-----+-----+ | 0 | 0 | 0 | 0 | PC-CRC |Cidx2|Cidx1| Octet 14 +-----+-----+-----+-----+-----+-----+-----+-----+ The codebook indices, VAD flag, pitch index, and class index are specified in Section 6 of [3]. The 4-bit CRC and the 2-bit PC-CRC in the FP MUST be calculated using the formula (including the bit-order rules) defined in 7.2.4 in [3]. Any number of FPs MAY be aggregate together in an RTP payload and they MUST be consecutive in time. However, one SHOULD always keep the RTP payload size smaller than the MTU in order to avoid IP Xie & Pearce Expires August 6, 2004 [Page 14] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 fragmentation and SHOULD follow the recommendations given in Section 3.1 in [10] when determining the proper number of FPs in an RTP payload. 3.3.3.2 Format of Null FP A Null FP for the ES 202 212 front-end codec is defined by setting all the 112 bits of the FP with 0's. Null FPs are sent to mark the end of a transmission segment. Details on transmission segment and the use of Null FPs can be found in [10]. 3.3.4 RTP header usage The format of the RTP header is specified in [8]. This payload format uses the fields of the header in a manner consistent with that specification. The RTP timestamp corresponds to the sampling instant of the first sample encoded for the first FP in the packet. The timestamp clock frequency is the same as the sampling frequency, so the timestamp unit is in samples. As defined by ES 202 212 front-end codec, the duration of one FP is 20 ms, corresponding to 160, 220, or 320 encoded samples with sampling rate of 8, 11, or 16 kHz being used at the front-end, respectively. Thus, the timestamp is increased by 160, 220, or 320 for each consecutive FP, respectively. The DSR payload for ES 202 212 front-end codes is always an integral number of octets. If additional padding is required for some other purpose, then the P bit in the RTP in the header may be set and padding appended as specified in [8]. The RTP header marker bit (M) should be set following the general rules for audio codecs as defined in Section 4.1 in [9]. The assignment of an RTP payload type for this new packet format is outside the scope of this document, and will not be specified here. It is expected that the RTP profile under which this payload format is being used will assign a payload type for this encoding or specify that the payload type is to be bound dynamically. 4. IANA Considerations For each of the three ETSI DSR front-end codecs covered in this document, a new MIME subtype registration is required for the corresponding payload type, as described below. Xie & Pearce Expires August 6, 2004 [Page 15] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Media Type name: audio Media subtype name: dsr-es202050 for ES 202 050, dsr-es202211 for ES 202 211, and dsr-es202212 for ES 202 212 front-end, respectively. Required parameters: none Optional parameters: rate: Indicates the sample rate of the speech. Valid values include: 8000, 11000, and 16000. If this parameter is not present, 8000 sample rate is assumed. maxptime: see RFC3267 [7]. If this parameter is not present, maxptime is assumed to be 80ms. Note, since the performance of most speech recognizers are extremely sensitive to consecutive FP losses, if the user of the payload format expects a high packet loss ratio for the session, it MAY consider to explicitly choose a maxptime value for the session that is shorter than the default value. ptime: see RFC2327 [6]. Encoding considerations: This type is defined for transfer via RTP [8] as described in Sections 3 and 4 of RFC XXXX. Security considerations: See Section 6 of RFC XXXX. Person & email address to contact for further information: Qiaobing.Xie@motorola.com Intended usage: COMMON. It is expected that many VoIP applications (as well as mobile applications) will use this type. Author/Change controller: * Qiaobing.Xie@motorola.com * IETF Audio/Video transport working group 4.1 Mapping MIME Parameters into SDP The information carried in the MIME media type specification has a specific mapping to fields in the Session Description Protocol (SDP) [6], which is commonly used to describe RTP sessions. When SDP is used to specify sessions employing ES 202 050, ES 202 211, or ES 202 Xie & Pearce Expires August 6, 2004 [Page 16] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 212 DSR codec, the mapping is as follows: o The MIME type ("audio") goes in SDP "m=" as the media name. o The MIME subtype ("dsr-es202050", "dsr-es202211", or "dsr-es202212") goes in SDP "a=rtpmap" as the encoding name. o The optional parameter "rate" also goes in "a=rtpmap" as clock rate. If no rate is given, then the default value (i.e., 8000) is used in SDP. o The optional parameters "ptime" and "maxptime" go in the SDP "a=ptime" and "a=maxptime" attributes, respectively. Example of usage of ES 202 050 DSR: m=audio 49120 RTP/AVP 101 a=rtpmap:101 dsr-es202050/8000 a=maxptime:40 Example of usage of ES 202 211 DSR: m=audio 49120 RTP/AVP 101 a=rtpmap:101 dsr-es202211/8000 a=maxptime:40 Example of usage of ES 202 212 DSR: m=audio 49120 RTP/AVP 101 a=rtpmap:101 dsr-es202212/8000 a=maxptime:40 5. Security Considerations Implementations using the payload defined in this specification are subject to the security considerations discussed in the RTP specification [8] and the RTP profile [9]. This payload does not specify any different security services. 6. Acknowledgments The design presented here is based on that of [10]. Normative References [1] European Telecommunications Standards Institute (ETSI) Standard ES 202 050, "Speech Processing, Transmission and Quality Xie & Pearce Expires August 6, 2004 [Page 17] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Aspects (STQ); Distributed Speech Recognition; Front-end Feature Extraction Algorithm; Compression Algorithms", (http:// pda.etsi.org/pda/) , October 2002. [2] European Telecommunications Standards Institute (ETSI) Standard ES 202 211, "Speech Processing, Transmission and Quality Aspects (STQ); Distributed Speech Recognition; Extended front-end feature extraction algorithm; Compression algorithms; Back-end speech reconstruction algorithm", (http:// pda.etsi.org/pda/) , November 2003. [3] European Telecommunications Standards Institute (ETSI) Standard ES 202 212, "Speech Processing, Transmission and Quality aspects (STQ); Distributed speech recognition; Extended advanced front-end feature extraction algorithm; Compression algorithms; Back-end speech reconstruction algorithm", (http:// pda.etsi.org/pda/) , November 2003. [4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [6] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [7] Sjoberg, J., Westerlund, M., Lakaniemi, A. and Q. Xie, "Real-Time Transport Protocol (RTP) Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs", RFC 3267, June 2002. [8] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003. [9] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 3551, July 2003. [10] Xie, Q., "RTP Payload Format for European Telecommunications Standards Institute (ETSI) European Standard ES 201 108 Distributed Speech Recognition Encoding", RFC 3557, July 2003. Informative References [11] European Telecommunications Standards Institute (ETSI) Standard ES 201 108, "Speech Processing, Transmission and Quality Xie & Pearce Expires August 6, 2004 [Page 18] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Aspects (STQ); Distributed Speech Recognition; Front-end Feature Extraction Algorithm; Compression Algorithms", (http:// webapp.etsi.org/pda/) , April 2000. Authors' Addresses Qiaobing Xie Motorola, Inc. 1501 W. Shure Drive, 2-F9 Arlington Heights, IL 60004 US Phone: +1-847-632-3028 EMail: qxie1@email.mot.com David Pearce Motorola Labs UK Research Laboratory Jays Close Viables Industrial Estate Basingstoke, HANTS RG22 4PD UK Phone: +44 (0)1256 484 436 EMail: bdp003@motorola.com Xie & Pearce Expires August 6, 2004 [Page 19] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Xie & Pearce Expires August 6, 2004 [Page 20] Internet-Draft RTP Payloads for ETSI DSR Codecs February 2004 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Xie & Pearce Expires August 6, 2004 [Page 21]